The former is a developer rom, the latter is a stable rom.
For Stable ROMS version means MIUI major.minor version.
For Developer ROMs, version is just the release date, e.g. 6.3.11 = 2016-03-11 So you can't compare two version of different branches from their version number.
all version are pretty much the same,there is no difference.
in last 30 version (weekly, and stable) they didn't solve battery drain, yellow display, noise and dots in pictures in low light environment, pocket dials, tap unlock ...............etc.
In each new version they spoil something that was previously working very well.